During the winter months, most houses and dwellings are sealed tight to prevent heat loss and often the homeowner has installed energy efficient windows, extra wall and ceiling installation and replaced worn weather stripping. All this directly benefits the homeowner by curing drafty doors and windows and limits heat loss through walls and ceilings so that the homeowner incurs less cost to heat the house. However, sealing the home against heat loss creates another problem. The air in the house becomes stale. Even though the air is recirculated, it contains cooking odors, smoke, cleaning sprays and other household pollutants and also may harbor germs and viruses. One solution to this problem is to change the air.
In a forced warm air heating system, room air circulates through the house giving up its heat and returning through the the return air ducts and filter back to the furnace. In the furnace, a blower forces the air over a heat exchanger and the air flows from the heat exchanger through ducts that spill the air through room registers into the rooms of the house. The furnace flue carries unburned gas and particulate matter to the house chimney through which the gas rises and spills into the atmosphere. Clearly, the furnace combustion area heat exchanger and flue are all sealed so that no products of combustion can leak from any of these parts into the house or into the warm air heating system and all flue gas flows up the chimney and into the atmosphere outside, usually above the roof of the house.
Heretofore, flue gas to air heat exchangers have been employed for pre-heating the combustion air to a furnace of the central heating unit of a house. Usually, the central heating unit furnace is in the ground or basement part of the house and draws upon air from inside the house for combustion in the furnace. Efforts are sometimes made to pre-heat the air before combustion, using a flue gas to air heat exchanger in the flue stack from the furnace. Heretofore, a great deal of effort has been made to provide such a heat exchanger that is both efficient and economical in cost and installation. With such a pre-heater, flue gas leaking into the combustion air does not cause a problem or danger to the occupants of the house, so long as all of the pre-heated air flows into the furnace combustion chamber and none leaks into the house. The present invention has no intention of improving upon such heat exchangers or of improving combustion operation or efficiency of a furnace.